GS2971 Datasheet, PDF (87/148 Pages) Semtech Corporation – 3Gb/s, HD, SD SDI Receiver, with Integrated Adaptive Cable Equalizer complete with SMPTE Audio and Video Processing

current 5-frame sequence. The de-embedder then re-locks to the new 5-frame
sequence, at which point a sample may be lost.
NOTE: In SD, all four channel pairs must follow the same 5-frame sequence.
4.19.3.3 Audio FIFO Block
The function of the FIFO block is to change the audio data word rate from the ANC rate
multiplexed with the video signal to the 48kHz audio output rate.
The audio FIFO block contains the audio sample buffers; one per audio channel. Each
buffer is 36 audio samples deep. At power up or reset, the read pointer is held at the zero
position until 26 samples have been written into the FIFO (allows for 6 lines per frame
with no audio samples; a maximum of 4 samples per line in SD Mode). See Figure 4-44.
Read
Pointer
Address 0
25
35
Audio Buffer
Write
Pointer
Figure 4-44: Audio Buffer After Initial 26 Sample Write
The position of the write pointer with respect to the read pointer is monitored
continuously. If the write pointer is less than 6 samples ahead of the read pointer (point
A in Figure 4-45), a sample is repeated from the read-side of the FIFO. If the write pointer
is less than 6 samples behind the read pointer (point B in Figure 4-45), a sample is
dropped. This avoids buffer underflow/overflow conditions.
Read
Pointer
Address 0
5
29
35
Audio Buffer
A
B
Write
Pointer
Figure 4-45: Audio Buffer Pointer Boundary Checking
Write
Pointer
The repeat or drop sample operation is performed a maximum of 28 consecutive times,
after which the audio outputs are muted (all sample data set to zero). In SD Mode, 26
samples are required to be written into the FIFO prior to starting the read operation
again.
GS2971 3Gb/s, HD, SD SDI Receiver
Data Sheet
45898 - 2
September 2012
87 of 148